Embryonic development of Eucorydia yasumatsui Asahina,with special reference to external morphology (Insecta: Blattodea,Corydiidae)

As the first step in the comparative embryological study of Blattodea, with the aim of reconstructing the groundplan and phylogeny of Dictyoptera and Polyneoptera, the embryonic development of a corydiid was examined and described in detail using Eucorydia yasumatsui . Ten to fifteen micropyles are localized on the ventral side of the egg, and aggregated symbiont bacterial “mycetomes” are found in the egg. The embryo is formed by the fusion of paired blastodermal regions, with higher cellular density on the ventral side of the egg. This type of embryo formation, regarded as one of the embryological autapomorphies of Polyneoptera, was first demonstrated for “Blattaria” in the present study. The embryo undergoes embryogenesis of the short germ band type, and elongates to its full length on the ventral side of the egg. The embryo undergoes katatrepsis and dorsal closure, and then finally, it acquires its definitive form, keeping its original position on the ventral side of the egg, with its anteroposterior axis never reversed throughout development. The information obtained was compared with that of previous studies on other insects. “Micropyles grouped on the ventral side of the egg” is thought to be a part of the groundplan of Dictyoptera, and “possession of bacteria in the form of mycetomes” to be an apomorphic groundplan of Blattodea. Corydiid embryos were revealed to perform blastokinesis of the “non‐reversion type (N)”, as reported in blaberoid cockroaches other than Corydiidae (“Ectobiidae,” Blaberidae, etc.) and in Mantodea; the embryos of blattoid cockroaches (Blattidae and Cryptocercidae) and Isoptera undergo blastokinesis of the “reversion type (R),” in which the anteroposterior axis of the embryo is reversed during blastokinesis. Dictyopteran blastokinesis types can be summarized as “Mantodea (N) + Blattodea [= Blaberoidea (N) + Blattoidea (R) + Isoptera (R)]”.     

The Happy Hen on Your Supermarket Shelf

This paper investigates what “free-range” eggs are available for sale in supermarkets in Australia, what “free-range” means on product labelling, and what alternative “free-range” offers to cage production. The paper concludes that most of the “free-range” eggs currently available in supermarkets do not address animal welfare, environmental sustainability, and public health concerns but, rather, seek to drive down consumer expectations of what these issues mean by balancing them against commercial interests. This suits both supermarkets and egg producers because it does not challenge dominant industrial-scale egg production and the profits associated with it. A serious approach to free-range would confront these arrangements, and this means it may be impossible to truthfully label many of the “free-range” eggs currently available in the dominant supermarkets as free-range.     

Microvilli on sea urchin eggs: a second burst of elongation

A scanning EM study reveals about 300,000 microvilli on each egg of the sea urchin Strongylocentrotus droebachiensis. The microvilli are about 0.2 μm long before fertilization, elongate to about 0.5 μm soon after fertilization (the “first burst” of microvillus elongation), and subsequently elongate again about midway between fertilization and first cell division (the “second burst” of elongation). The second burst occurs during a discrete 30-min period and results in some microvilli being as long as 10 μm, although the average length is about 1.8 μm. The surface area of the egg following the second burst is about 2.7 times the area of the unfertilized egg.     

Die Cytologie der Parthenogenese bei dem Tardigraden Hypsibius dujardini

Hypsibius dujardini Doy. (Articulata, Tardigrada) shows obligatory parthenogenesis under given cultivating conditions. Males were never found. The first meiotic division reduces the number of chromosomes; the (2n=10) chromosomes are divided between a small polar body and the egg nucleus. Prior to the second division the dyads divide, thus restoring the diploid number. A diploid polar body is formed subsequent to the second division. After the egg nucleus has moved toward the center of the egg, the cleavage divisions begin. — During meiosis II and the first cleavage divisions the chromosomes can develop into “large chromosomes” which presumably consist mostly of RNA. No “large chromosomes” are found after the seventh cleavage division. Sometimes a plate of coloured material (“elimination chromatin”) can be observed between the anaphase daughter plates of the first cleavage divisions. In this case the chromosomes are always small.     

Maternal effects in Daphnia: what mothers are telling their offspring and do they listen?

Maternal effects can significantly impact offspring performance. Provisioning of offspring with energy stores can quantitatively alter their growth rates, survivorship, and future fecundity, and influence population regulatory mechanisms. In this paper, we show that maternal effects can also qualitatively affect offspring reproduction (i.e. their mode of reproduction). The freshwater herbivore Daphnia pulex can change the amount of energy allocated between asexual and ephippial egg production. Our experiments on individuals, experiencing “step‐up” or “step‐down” food manipulations, reveal that offspring qualitatively shift their energy allocation away from asexual reproduction to ephippial egg production when there is a simple mismatch between maternal and offspring food environments. We show that the response is asymmetric with respect to changes in food level, ephippial egg production is higher with a greater mismatch between environments, and that the effect can be observed in dynamic experimental populations. These results point to a “generational memory” that could challenge our interpretation of field patterns and mechanisms influencing population dynamics in Daphnia–algal systems.     

Protein-bound SH groups in frozen-thawed egg cells of the sea urchin

Unfertilized egg cells of the sea urchin St. intermedius could survive slow freezing to ?15 °C for a short period of time, but at the same freezing temperature extracellular freezing became fatal within a few hours. Such freezing injury resulted in “black” or “white” cytolysis in frozen-thawed cells. “Black” cytolysis took place in the process of both freezing and thawing, while “white” cytolysis occurred only on thawing. Rapid rewarming consistently produced “white” cytolysis in extracellularly frozen cells. The observed behavior of the injured cells during freeze-thawing appeared favorable for the explanation of freezing injury by the SH-SS hypothesis. Protein-bound SH groups were quantitatively determined in both whole cell and cortex with plasma membrane before and after freeze-thawing. However, no significant change in the SH value was observed between freeze-thaw cytolysed materials and unfrozen ones.     

Egg structure and outline of embryonic development of the basal mantodean, Metallyticus splendidus Westwood, 1835 (Insecta,Mantodea, Metallyticidae)

The egg structure and outline of the embryonic development of Metallyticus splendidus of one of the basal Mantodea representatives, Metallyticidae, were described in the present study. The results obtained were compared with those from the previous studies, to reconstruct and discuss the groundplan of Mantodea and Dictyoptera. In M. splendidus, the egg is spheroidal, it has a convex ventral side at the center in which numerous micropyles are grouped, and it possesses a conspicuous hatching line in its anterior half. These are the groundplan features of mantodean eggs and the “grouped micropyles in the ventral side of the egg” are regarded as an apomorphic groundplan feature of Dictyoptera. A small circular embryo is formed by a simple concentration of blastoderm cells, which then undergoes embryogenesis of the typical short germ band type. Blastokinesis is of the “non-reversion type” and the embryo keeps its original superficial position and original orientation throughout embryonic development. During the middle stages of development, the embryo undergoes rotation around the egg's anteroposterior axis. These features are a part of the groundplan of Mantodea. It is uncertain whether sharing of the “non-reversion type” of blastokinesis by Mantodea and blaberoidean Blattodea can be regarded as homology or homoplasy.     

Hatching of the Anostracan Branchiopod Chirocephalus diaphanus Prévost I. Osmotic processes and the possible role of glycerol

An osmotic hatching mechanism is proposed for the Anostracan Branchiopod Chirocephalus diaphanus, Prevost. In this mechanism, glycerol is thought to accumulate in the egg as a result of the metabolism of the embryo. The osmotic pressure exerted by the egg, largely due to this glycerol accumulation, causes water to enter from the environment. Eventually the hydrostatic pressure thus generated is sufficient to cause rupture of the eggshell. It is recognised that hatching in this Anostracan is a two-staged phenomenon, a process of “breaking”, in which glycerol is involved, preceding true “hatching”, in which glycerol is not involved. The egg is described and the physiology and ecological significance of the proposed hatching mechanism are discussed.     

BREEDING SUCCESS IN SOME AFRICAN EAGLES RELATED TO THEORIES ABOUT SIBLING AGGRESSION AND ITS EFFECTS

Brown, L. H., Gargett, V. & Steyn, P. 1977. Breeding success in some African Eagles related to theories about sibling aggression and its effects. Ostrich 48:65-71. Previous explanations for fatal inter-sibling strife in eagles (lack of food, extra aggressiveness which enhances survival, and an expression of the innate aggressiveness or territoriality of raptors) can not be supported by recent evidence. The latest theory, that the second egg acts as a “reserve”, is examined. If so, eagles normally laying two eggs should have better reproductive success than eagles laying a single egg. However there was no significant difference between the mean reproductive success of five African eagle species that lay two eggs and that of five African eagle species laying one egg. Even excluding inequalities due to sample size, and other factors, the overall finding is the same. In Verreaux's Eagle Aquila verreauxi for which the largest number of records is available there was a significantly higher total loss in clutches recorded as c/l than in c/2 clutches, but the reasons for the laying of a one-egg clutch, and its success or failure, have not been investigated. In three out of 120 c/2 the second-laid egg acted as a “reserve”, but in 110 cases the second-laid egg was “wasted”. Direct evidence and a comparison of reproductive success between two-egg and one-egg African eagles does not support the latest theory, therefore inter-sibling strife which effectively reduces the clutch of two to one, is still inexplicable.     

On oviposition in weevils of the genus <Emphasis Type="Italic">Larinus</Emphasis> Dej. (Coleoptera,Curculionidae)

The following actions performed by females of several Larinus Dej. species during egg laying are described: search of an appropriate place on the plant, making the hole for the egg, oviposition proper, and sealing the hole. The hole preparation takes the longest time and the greatest effort. Only one individual usually completes development in one flower head. Females of Larinus vulpes Ol. prefer larger flower heads for oviposition and occasionally lay eggs into stems. The ability of females to distinguish the flower heads with already laid eggs is discussed. Species of Larinus may be divided into two groups with “early” and “late” oviposition. The evolution of egg laying in the genus Larinus is discussed.     

DIRECT AND CORRELATED RESPONSES TO SELECTION ON AGE AT REPRODUCTION IN DROSOPHILA MELANOGASTER

Aging may be a consequence of mutation accumulation or of negative pleiotropic correlations between performance late and earlier in the lifespan. This study used artificial selection on flies derived from two different base stocks to produce “young” and “old” lines, propagated by breeding from young and old adults respectively. Virgin and mated adults of both sexes from the “old” lines lived longer than “young” line flies. “Young” and “old” mated females did not differ in fecundity or fertility early in the lifespan, but “old” line females had higher fecundity and fertility late in life. The results therefore suggested either that the response to selection had revealed the effect of mutation accumulation, or that pleiotropy involving characters other than early fecundity must have been involved. Development time from egg to adult was longer in the “old” lines. Competition of selected line larvae from one base stock against mutant marked larvae from the same base stock revealed that, at a wide range of larval densities, “old” line larvae showed lower survival rates than “young” line larvae. Thorax length and wet weight were significantly greater in the “old” line flies from one base stock. The results may imply that the selection regime in the “old” lines favored extended growth during development to produce a more durable adult soma, despite the cost in increased larval mortality and delayed reproduction, because the potential reproductive benefits later in life were increased. However, the differences between larvae from “old” and “young” lines could also be attributable to density differences, and this possibility needs systematic investigation.     

Novel surface specialization on a sea anemone egg: “Spires” of actin-filled microvilli

The ultrastructure of the “spiny” surface of Tealia crassicornis eggs is examined in detail by scanning and transmission electron microscopy in order to understand its function. Long microvilli are clustered together in spiral aggregates of 50–75 microvilli called “spires.” There are about 15,000 spires per egg. Dense bundles of microfilaments making up the cores of these microvilli are shown to be composed of actin by staining with the fluorescent dye nitrobenzoxadiazole (NBD)-phallacidin. It is postulated that the bundles of actin and the spires of microvilli are stiff and provide reinforcement to the egg surface. Such postulated properties would provide physical protection for these large eggs which, unlike the eggs of most invertebrates, appear to lack all extracellular investing coats.     

An evolutionary interpretation of the “motivation to oviposit”

The ovipositional behavior of parasitoids and other insects is often described by phrases such as “motivation to oviposit” or “ovipositional drive”. This paper shows how an evolutionary (i.e. functional) interpretation can be given to such phrases. A detailed model for the parasitisation of Sycamore aphids by M. pseudoplatani is developed, using experiments by Collins and Dixon (1986). Two models are developed: i) one in which egg complement is the only state variable and ii) one in which egg complement and information concerning host densities are state variables. Comparisons of the behaviour of simulated parasitoids, using the decisions associated with the models, and the experiments suggest that both egg complement and information are important for the parasitoid's decision making. Accepting previously parasitized hosts may be optimal, and not simply an error in parasitoid perception. A number of other detailed predictions are made, such as the relative fitness of first and second eggs in superparasitized hosts and the nature of the memory of the parasitoid.     

INTRINSIC REPRODUCTIVE ISOLATION BETWEEN TWO SISTER SPECIES OF DROSOPHILA

Drosophila santomea and D. yakuba are sister species that live on the volcanic African island of São Tomé. Previous work has revealed several barriers to gene flow, including sexual isolation, hybrid sterility, and “extrinsic” ecological isolation based on differential adaptation to and preference for temperature. Here, we describe several new “intrinsic” barriers to gene flow—barriers that do not depend on the species’ ecology. These include reduced egg number, reduced egg hatchability, and faster depletion of sperm in interspecific compared to intraspecific matings. Further, hatching interval and egg‐to‐adult development time are significantly longer in interspecific than intraspecific crosses. If a female of either species is initially mated to a heterospecific male, she lays fewer and less‐fertile eggs than if she is first mated to a conspecific male, so that heterospecific matings permanently reduce female fertility. Finally, D. santomea females mated to D. yakuba males do not live as long as virgin or conspecifically mated females. The “poisoning” effects of heterospecific ejaculates may be byproducts of antagonistic sexual selection. Although these species diverged relatively recently, they are clearly separated by many isolating barriers that act both before and after mating.     

Bemerkenswerte endogene Farbveränderung der Eischale von Chioninia delalandii (Duméril & Bibron, 1839) (Reptilia: Sauria: Scincidae)

The paper describes an unusual endogenous eggshell colouration observed in an egg of the Cap Verde skink Chioninia delalandii.A female specimen, kept in a terrarium, laid three eggs. Two of them were considered as fertilized (oval germ-disk, weakly pink). They were embedded 1 cm deep in a layer of moistened clay granules (substrate/water 2:1) and kept under different temperatures (egg 1 “cool”, 26–27 °C; egg 2 “warm”, 29–30 °C). There was a normal embryonic development in both eggs from their volume-enlargement and characteristic allometric growth (egg wide > egg length). The young hatch after 51 and 56 days.A change in eggshell colour, however, occurred in the “warm” kept egg during the last third of its incubation period. It started with a small spot (2–3 mm) in the outer area of the animal egg pole and spread into a dark-violet colouration over the whole eggshell within 15 days. After hatching of the young the shells of both eggs were examined. In the non-coloured egg there was no great difference in colour between the inner and outer egg layer, while in the coloured egg there was a distinct difference between the inner part, which was dark violet-gray, and the pale gray calcareous deck-layer. From the macroscopic view along the edge of the eggshell it was not identifiable, if the colour pigment was infiltrated into protein fibrils of the condensed surface layer.A possible explanation for the eggshell colouration could be an unusual embryonic pigmentation. This assumption is based on the first appearance of a restricted, point-like coloured area and its further regular extension. It might be that dark pigments (melanophores?) reached the eggshell (membrana testacea) and infiltrated the border-area to the condensed surface layer.     

Switch in pattern formation after puncturing the anterior pole of Smittia eggs (Chironomidae, Diptera).

The aberrant pattern, “double abdomen,” previously induced in the egg of Smittia by uv irradiation of anterior pole regions was also produced by puncturing of the egg at the anterior pole. Double abdomens and embryos with anterior defects developed in eggs in which puncturing had locally prevented the regular arrangement of cleavage nuclei in the periplasm. The resulting gap in the blastoderm at the anterior pole was subsequently closed under exclusion of a small amount of egg material. Double abdomens did not develop in eggs where exclusion of anterior egg material was not observed. Thus a basic switch in the developmental program of the egg appears to depend upon the functional elimination of some crucial components in the anterior egg region.     

Mechanism of First Cleavage Specification in the Mouse Egg: Is Our Body Plan Set at Day 0?

In most animals the body axis is specified in the egg. Because of their highlyregulative capacity after experimental manipulations,1-4 mammalianpreimplantation embryos have long been thought to be an exception to this rule,lacking polarity until the blastocyst stage. However, it has recently been suggested5-7 that the embryonic-abembryonic (Em-Ab) axis of the mouse blastocyst arisesperpendicular to the first cleavage plane. Considering the second polar body (2pb)as a stationary marker for the “animal pole (A-pole)” during preimplantationdevelopment,5,6 the authors concluded that the polarity of the mouse embryo isalready specified in the egg, as is the case for most non-mammalian animals.5-7However, the results of our recent time-lapse recordings have shown8 that in 50 %of the embryos the first cleavage occurs at a considerable distance from the“animal-vegetal (A-V) axis” and that the 2pb moves towards the first cleavageplane, in contrast to the previous claims. Thus, there is no predetermined axis in themouse egg. We also presented a novel model for specification of the first cleavageplane: this is defined as the plane separating the two apposing pronuclei that havemoved to the center of the egg. In this review we will elucidate the discrepancybetween the previous model and our model, and discuss the possible causes.     

栽培甜菜卵细胞、合子及二细胞原胚的超微结构

为丰富被子植物生殖生物学资料, 并为甜菜相关研究提供参考, 应用透射电镜技术研究栽培甜菜(Beta vulgaris)卵细胞、合子和二细胞原胚的超微结构特征。结果如下：在成熟卵细胞中多聚核糖体数量不多, 且细胞代谢活性较弱; 初期合子内, 核仁大量合成核糖体前体物质, 胞质中多聚核糖体数目众多, 细胞代谢活性较强; 休眠期合子的核仁变小, 胞质中核糖体数量急剧减少, 仅有少量多聚核糖体, 细胞代谢活性较弱; 合子分裂前期和二细胞原胚期, 核仁显著, 胞质中核糖体的密度增加, 出现大量多聚核糖体, 细胞代谢活性较强。根据上述结果可以得出, 栽培甜菜从卵细胞成熟→合子初期→合子休眠期→合子分裂前期→二细胞原胚的超微结构变化中多聚核糖体的变化最为显著, 表现为“少→多→少→多”的数量变化过程, 反映出细胞代谢状态也经历了“弱→强→弱→强”的变化过程, 这种变化趋势与配子体世代向孢子体世代转变有关。     

OCCURRENCE AND DEVELOPMENT OF A FILIFORM APPARATUS IN THE EGG OF PLUMBAGO CAPENSIS

Micropylar wall extensions in the egg of Plumbago capensis arise as small pegs of periodic acid-Schiff's-positive material soon after the egg is organized. These inward projections of egg wall increase in size, becoming extensive near anthesis. Some branching of the filiform apparatus occurs. In mature embryo sacs the micropylar portion, with the lowermost portion of the egg included, becomes entrenched in the nucellus. The possible significance of this “gametic transfer cell” is discussed in relation to the apparent absence of synergids from the reduced embryo sac of Plumbago.